Cavity resonator electron discharge apparatus



w. w. HANSEN x-:TAL 2,578,699

CAVITY RESONATOR ELECTRON DISCHARGE APPARATUS Original Filed Aug. 24,19'39 l az l @hqhmil lgi//M L 7# TTORNEY Patented Dec. 18, 1951 CAVITYRESONATOR LECTRON DISCHARGE APPARATUS William W. Hansen and Russell H.VarianStan ford University, Calif., assignors to The Board of Trusteesof The Leland Stanford Junior University, Stanford University, Calif., alegal entity of California Application December 6, 1943, Serial No.513,002, which is a division of application Serial No. 291,652, August24, 1939. Divided and this application October 3, 1947, Serial No.777,801

This invention relates to hollow cavity resonator electron dischargeapparatus and is particularly concerned with structural and 'circuitimprovements in such apparatus.

This is a division of our Patent No. 2,460,288 for Resonator Apparatus,iiled December 6, 1943, as a division of application Serial No. 291,652,filed August 24, 1939, for Dielectric Guide Signaling, now Patent No.2,375,223.

It is a major object of the invention to provide i hollow cavityresonator electron discharge apparatus having adjustable energy couplingarrangements.

A further object of the invention is to provide novel hollow cavityresonator electron discharge apparatus wherein a suitable member isshiftably mounted in the electromagnetic eld of a hollow resonatordevice having an evacuatedsection through which an electron beam ispassed in such fashion that coupling of said member with the eld may becontrollabl'y varied from outside the device without disturbing thevacuum seal.

A further object of the invention is to provide hollow cavity resonatorelectron discharge apparatus wherein a `shiftable conductive, memberterminating a high frequency transmission line extends within a hollowresonator for variable coupling with the high frequency field withinsaid resonator, that part of the resonator eld with which said member iscoupled being sealed off from the remainder of the resonator interior byvitreous or like wave-energy-permeable wall means permitting saidcoupling. Speciiically the coupling member may be rotatable for changingthe amount of energy transfer between the transmission line and saideld.

It is a further object of the invention to provide hollow resonatorapparatus wherein an evacuated hollow resonator device is connected in anovel mannerto an electromagnetic wave energy conducting means throughuse of a vitreous seal.

Further objects of the invention will presently appear as the4description proceeds in connection with the appended claims and theannexed drawings, wherein:

Figure 1 is a side elevation partly diagrammatic and partly in sectionof hollow cavity resonator electron discharge apparatus embodying thein- Vention as used for amplifying signals projected along a dielectricwave guide; and

Figure 2 is a side elevation of a further embodiment of 'the inventionwherein Wave .guide r15l claims. (allais- 39) Cil sections are directlycoupled to the resonators of an amplier.

The term hollow as used herein in describing resonators and dielectricor hollow-pipe wave guides is of course intended to embrace all suchresonators and dielectric or hollow-pipe wave guides regardless `ofwhether the dielectric therein is air or some other medium.

Fig. 1 illustrates relaying apparatus including a hollow resonatordevice I I for picking up a signal traversing a wave guide I2 from leftto right, amplifying the signal and then reradiating the same forcontinued transmission along the wave guide. This'relaying apparatusincludes directional discriminating means for receiving the signal to berelayed and for reradiating the signal after it has been amplified. Therelaying apparatus is not responsive to signals coming from a directionlopposite to its direction of sensitivity and hence will not causeinterference with .signals traversing the guide in that oppositedirection. Ordinarily a similar relaying device with oppositedirectional characteristics is ernployed in the wave guide for relayingsignals in the opposite direction, as described and claimed in saidPatent No. 2,375,223.

Spac'ed signal receiving meansi and lL'which may be of any suitable typesuch as the illustrated dipole antennae, are suitably located in waveguide I2. A phase shifter designated at I5 is supplied from antenna i3,while an amplitude adjuster designated at I6 is supplied from 'antennaI4. The outputs of the phase shifter and amplitude adjuster are combinedas illustrated in hollow resonator device Il which is anultrahigh-frequency amplifier. The output of ampliiler I I is suppliedthrough a second phase shifter Il and amplitude adjuster I8 toreradiating antennae I9 and 2|.

Phase shifter i5, connected to receiving' antenna I3, is illustrated asa concentric transmission line which is adjustable as to length. Aconcentric line portion 22 which is shiftable axially of wave guide I2extends through an opening 23 provided in wave guide I2 and has dipolei3 connected with its upper end. The lower end of concentric lineportion 22 is provided with a female socket for telescopingly receivingthe upper end of a relatively iixed concentric line portion 24. A screw25 having a knob 26 is threaded into a bracket 2l fixed on wave guide- II. Screw 25 is rotatably mounted on a lug 28 integral with line portion22, and is otherwise so connected With lug 28 that rotation of knob 26varies the axial distance between dipoles I3 and i4, therebyvr varyingthe phase difference between these dipoles within the wave guide. Theconcentric line connecting dipole I3 to amplier II is thereby changed inlength so that rapid changes in phase of the outputs of the two dipolesas supplied to the amplifier may be effected by adjusting phase shifterI5.

Concentric line portion 24 terminates in a conductive loop 3| which isxcoupled to deliver energy to amplifier I I as will be described.

Amplitude adjuster I6 comprises an upper concentric line portion 32connected to receiving antenna I4 after extending through a suitableaperture in wave guide I2. The lower end of line portion 32 is formed asa female socket which is rotatably connected with the mated upper end ofa short concentric line portion 33 having a manual operating knob 34. Atits lower end concentric line portion 33 terminates in a conductive loop35 which is coupled to deliver energy to amplifier I I as will bedescribed.V Thus loop 35 is rotatably mounted with respectl to theconcentric line between antenna I4 and amplier II.

Amplifier II preferably is generally of the cascade type disclosed inUnited States Letters Patent No. 2,280,824, issued April 28, 1942.Amplier II comprises a plurality of aligned interconnected dielectric orcavity resonators 36, 31

and 38 which are evacuated. Within a vitreous insulating cup 39 at oneend of the amplifier is provided a cathode 48 surrounded by a focusingshield 4I, said cathode being indirectly heated by a heater coil 42 thatis supplied from the battery 43. The electrons released by the cathode40 are drawn in a columnar stream by a strongly positive grid 44,which-grid is held positive with respect to the cathode by a battery 45.Note that the positive side of the battery 45 is grounded, which is alsotrue of the casing of amplifier II, to which casing grid 44 isconnected. The electron stream drawn through grid 44 passes throughsubsequent pairs of grids 46, 41, 48, 49, and I, 52, constituting gridsof hollow resonators 36, 31 and 38, respectively. After leaving grid 52,the electron stream passes through additional inclined parallel grids 53and 54 to a collector and detector plate 55.

Loops 3| and 35 are both disposed within input resonator 36, so as to'be coupled in energy exchanging relation with the electromagnetic fieldof the resonator as will be described. A suitable vacuum tight sealedjoint employing a body of vitreous material as indicated at 56 isprovided Where concentric line portion 24 is joined to resonator 36.

A partition 51 of vitreous material is provided within resonator 36 soas to seal off that section of resonator 36 within which rotatable loop35 is disposed from the remainder of the resonator interior. Partition51 is of course made of a material which is permeable to the resonatorfield and permits the resonator field to couple with loop 35. Asillustrated, partition 51 provides an outwardly facing pocketaccommodating loop 35.

Resonator 38 is also provided with a frequency control device indicatedat 58 comprising a glass or like vitreous pocket or envelope 59, theclosed end of which extends well into the interior of resonator 36. 'Iheopen outer end of pocket 59 is sealed off along the edge of a suitableaperture in resonator 36, as illustrated, so as to be vacuum-tight. Ametal plug 6I is suitably mounted for longitudinal advance or retraction4 within pocket 59, as by rotation of nut 62. Similar frequency controldevices 63 and 64 are provided on resonators 31 and 38, respectively.

Within output resonator 38, conductive loop 65 is disposed in a sectionof the resonator which is sealed off from the remainder of the resonatorinterior by a vitreous partition 66 similar to partition 51. Loop 65,like loop 35, is rotatable for variable coupling with the associatedresonator field. Manual knob 61 of amplitude adjuster I8, which isstructurally the same as amplitude adjuster I6, is provided forselective rotation of loop 65. Loop 65 is thus connected to transmittingantenna 2| in the same manner that loop is connected to receivingantenna In like manner conductive loop 68 within resonator 38 isconnected to transmitting antenna I9 through phase adjuster I1 which isidentical in construction and operation to phase adjuster I5.

Thus in each of resonators 36 and 38, the electrically conductive innersurfaces of the resonators substantially define envelopes bounding theelectromagnetic fields. The conductive loops and shiftable frequencycontrol elements are all at least in part disposed within the physicalconfines of those envelopes, for coaction with the fields. The rotatablecoupling loops are disposed in non-evacuated sections of the envelopes.

As illustrated loops 35 and 65 may be inserted into or withdrawn fromtheir associated resonators without impairing the vacuum seal of theresonators.

During operation, the indicated wave energy traveling along wave guideI2 from left to right is picked up by receiving means I3 and I4 anddelivered to resonator 36 in in-phase relation.v

'Ihis received energy serves to excite resonator 36 in such mode that analternating current electric field is established within resonator 36and between grids 46 and 41, the said electric eld serving toalternately impart positive and negative accelerations to successiveelectrons of the stream passing therebetween; thereby causing theelectrons of the stream to traverse the space between resonator 36 andthe next resonator 31 with cyclically varying velocities. The fasterelectrons which passed through the electric eld later than the precedingelectrons will tend to overtake the latter in the interspace betweenresonator 36 and resonator 31, so that by the time the electron streamhas arrived at grid 48, the stream will have a slight periodic variationin electron density at the frequency of the field between grids 46 and41.

' If intermediate resonator 31 is properly tuned, which is accomplishedby tuning means 63, an alternating electric eld will be establishedbetween grids 48 and 49, which is much stronger than that existingbetween grids 46 and 41, with the result that the successive electronswill receive much larger variations in velocity than that previouslypossessed, thereby effecting still greater bunching and correspondingincrease in variation in electron density during passage through thespace between resonators 31 and 38. Similarly, the entrance of thestream of variable electron density into resonator 38 establishes astrong alternating electric field between grids 5I and 52 which acts toretard the electrons so that they do work upon this field and therebymaintain the alternating electromagnetic field within resonator 38 andenergy from the field is picked up by loops 68 and 65 and reradiatednovatonlong Awave guide H12 :by itransinitting mreans H59 iandzt; n

Grid 53, being at the potential of .the .:positive.sidef.ofibattery:,45, aidsinimaintaininguthefstream in :coimnnar iform,whereas :inclined sgrid rfid .is preferably maintained at 1a .potentialmear ethat o'f .the cathode 'ilhis accomplished-:by luseroipotentiometer ffii) :and battery ill :connected sto cathode :lead .'12,Withxgridr'lrat this ipotential, 4most-.of the .electrons -:arerreflected '-back rand Pto one side, and only the speededeupelectronswill pass through this grid. Thusfas theychangein ,electronNelocityincreases, morefanrii-more iof the 'faster ielectrons will:reach plate .55 beyond .grid 54, while fevver of the slower `electronswill rreach :this `fplate. `the *current therefore :reaching ,plate 55`increases .as the amplitude of joscillations .in .the hollow resonatordevice increases, iso that said `dev-ice asa whole serves-.as a .cascade,ampli- 'fler1and..detector. d

YIhe 4detected signal on the -plate -55 isfinore .negative the.strong-er .fthe-oscillations rbecome. Looked atinano'therway.as.thevcurrentthrough the :plate circuit increases,1.tl-iedrop,across .a re- .sistor ".I3 .in .the .plate .circuitincreases, thereby i lowering the potential .at plateZ `whirinis shownconnected through-.5a lbias'ing :battery .it and lead .75 .toa grid .1E,positioned fin rfront -of emitter 4I). Thus the .potential .of rgrid'IB lis correspondinglylowered, .effecting .a .decrease in the currentpassing .through the device flue to the repellent .action of vthe gridll on the .electron stream. Thus, since plate 55 becomes .more .neg-Vati-ve .as the signal Iintens'ity increases, grid It `acts as :anautomatic volume control serving -to m.

As above described, the tuning devices 'sup` plied 'to each 'resonatorconsist of vitreous en.- velopes 59 that Vextend .into 'the resonators-and ,prevent .theiadm'ission of 'airth'ereinto I `The `-posi- 'tion inwhich the envelopes 'T59 andthe associated metal Aplugs project 'intoVthe resonators has an I'important bearing on `the tuning.. If theVmetal plug is 'positioned in Va .part of the resonant cavity containing'essentially 'electric field, 'the Y.1o-lug serves to increase thecapacity of the 'cir' 't'.so that the resonant :frequency will bedecreased; whereas if this plug is inserted in .a're'gion containingmostly magnetic held, it reduces the total volume of magnetic 4field.since 'theplug contains no iield, whereby Jvthe inductance will be de;creased 4and the Vfrequency will be increased fit is therefore possibletoiind an'interrnediate point where the mere presence of the 'plug will.not :affect the frequency. `As illustrated 'in Figure l, fthe metalplugs are located where the magnetic field 'is strong. As the plugs aremoved in' and 'out, controlled changes "in the `resonantfrequency of theresonators is obtained, there'byallowing vthe various resonant Achambers'36 `to v3B to' be ftuned to the incoming signal.

Rotation of loop 35 by 'manipulation *of knob 134 alters Athe number ofmagnetic lines "oi" 'altere mating current flux .resonant'inhollow'resonator 33 'that 'are enclosed by 'the loop, thereby varyingthe intensity of the signal that is-`set up in resonator 36 .byagivensignal passing'along Ware guide `I2 fromfleft to right. Similarly,rotation -of loop 155 by .rotation of `knob 6'! 4varies -the 'intens'ityof the amplified signal dfelivered to waive guide I2.

Thus energy traveling from left tofri'ght along waveguide I2islpickedupiby receiving antennae I3., Illfand deliveredtocaseadeeniplifierf-H'. 'T-n'e 'amplfredisignal is in 'tu1:narerauiatedin theforigina-l direction alongivvaveaiguide .I 2 drum antennae I9, ZI.kv'Suitalo'le phase @and `:amplitude iadus-tments areprovided fat F'bcththe :input rand i output of fainpliiier .'Izimand 1 an automatic volumeVcontrol is providedjior varying -the :amplification tinversely to'variations-in amplitude of the-received signal;

.Beceivingantennae I3 .and .M rare ,preferably located about-fone-quarter Wave length fanart withinwavefguide I.2,; that is, theyrare :spaced a distance apart :such ythat fthe waves .received byantennae t3 and fI-tare :substantially 90 apart in `fphase 1due `tothetime l:consumed by the wave travel-ing this distance. .Phase shifterI5 :is adjusted ,by ti1rni-ngitsfcontrol .knob .25 so.=that the.electromagnetic .waves delivered vtherefrom toresonaton38-.are.phasewith the lwaves -delivered toresonator r36 `fromthe amplitude adjuster `I6 when `the received electromagnetic waves are'traveling from-.left to right wave guide ,I`2.`..'Ihus, though .theantenna AIltis displaced yone-quarter 'wave .length from antenna I 3.,the output of -amplitude adjuster '1I 6 is .phased with the "signallreceived 'from the phase shifter E5.. 4`"Thus, "the 'outputsojante'iin'ae `I3 and .I4 fare corfnbiiiedfadditively'for 'supplyingultranignffrequeney amplifier .11.

However, 'Should a .signal'be received by antennae. lll'and 1.3, coming"from the reverse direjction, "that'is, moving from 'right-to leftin'Figuitel, 'then in that case .'the electromagnetic waves"received at"I3 will be 90 displaced "later tnanfthoseireceiveii at T4, and sincephase vshifter I5 and 'theconnections shown .act to retard the phase "ofthe output of'a'ntenna I3 `-90 more, the output of the phasefsliifteryI5 will be directly out of. phase vwith 'that supplied resonator 3'16from amplitude adjuster f6. .'llhus, lthese .reversely movingsignalsw'ill tend to cancel each other. `If

the amplitude of 'these reversely moving signals is 'made identical byadjusting `the`knob 3iA of amplitude adjuster I6, Vthe effect of thesignal com'in'gf'frornftheright atiamplier I `I will be zero duev tothe.'canceiling of the opposite signals. Thus, "if receiving -means I3.and I4 .are -approxiinately 'one-quarter Wave length apart iin theguide, their 'combined vsensitivity .in one direction, e., ifor'signalsjmovingfrom the left ltovvard lthe right, .will vbesubstantially a maximum, whereas 'for signalsmovingin the oppositedirection the conbined 'se sjiti'vityzwillbe zero. YIt is notesseri'tial that these receiver'means 'be exactly onequarter wave lengthapart, as some .departure ,from` thisvalue will not appreciably 'affectthe sensitivity o'f fthe system. Since it is necessary 'that theLsensitivity of the apparatus 'to signals traversing the guide in 'thereverse direction should be as 'near zero as possible, 'the receiving'means are 'set up, 'inpractice as near one-quarter Wave length apart asconvenient, or 'some bdd multiple thereof. The final elimination '0f thesen itivity ftofilow in `'the Wrong 4direction is ob- -tainedbyfiine'fadjustlnent 'of the phase shifter knob 26a-nd theja-'rnplitudeVadjuster knob 34.

"Phase shifter 4I *I 'acts to retard the Vphase ofthe Waves i"emittedifrom antenna I 9 by 90 relative to thesphase of the wavesemitted fromantenna 2 I.

`is :spaced along'vvave Vguide 'f2 about 'onev'cliaiter' wave 4lengththerefrom, so 'that by the time the waves yfrom'antenna 21 have reachedantenna ISQ'tfhe' combined waves are in phase "for `(tra'n'sinfissi'onalongivavefg'uide I2 Ytciw'ard the right; 'Antennae "I9 Jand 2l, ontheother hand,

75 aresub'traetive their action so iar as transmission to the left isconcerned. ,Thus, radiation from antenna I9, upon reaching antenna 2|,will be displaced 90 from that which would be received at antenna 2|were phase shifter |1 not used, but since phase shifter I 1 retards thephase by 90 more, the net'result is to establish an 180 out-of-phasecondition between the signal emitted at I9 and that received at 2| fromI9, so that these two signals cancel out and hence do not traverse thewave guide toward the left, i. e., in the wrong direction. Furtheraction of the relaying and associated apparatus in connection withultra-high-frequency energy transmission is disclosed and claimed inSaid Patent No. 2,375,223, to which reference is made for furtherdetail. The present'invention is concerned mainly with above-describedfeatures relating to the amplifier and associated arrangements.

In Figure 2 an electron-beam-excited hollow resonator device 18 isdirectly connected between Wave guide sections 19 and 8| to relay andsimultaneously amplify a signal passing from left to right along thewave guide.

Device 18 is here a two-resonator amplifler, embodying a hollow inputresonator 82 similar to input resonator 36 and an output resonator 83similar to`output resonator 38 in Figure 1. Resonator. 82 is providedwith spaced grids 84, l85 and resonator 83 is provided ,with spacedgrids 8B, .81. Tuning devices 88 and 89, similar to that at 58, areprovided for resonators 82 and 83. As indicated by correspondingreference numerals, the various electrode and automatic volume controlarrangements are the same in Figure 2 as in Figure 1. Device 18 has nointermediate cascade amplierresonator such as that at 31 of Figure 1 andhence operates similarly'to the usual tworesonator amplifier disclosedin United States Letters Patent No. 2,242,275. Hence amplifier 18 issimilar to amplifier I I, except for details of coupling to the waveguide which will' be described below. l v

Output resonator 83 is formed with an energy output aperture |88 sealedby a glass or like wall |89. The adjacent end of wave guidesection 8| isslotted to permit passage of an apertured gate plate 9| having aperture92 adapted to register with aperture 88. Thumb screw 93 opposing aspring 94 is adapted toadjust plate 9| vertically to thereby varytheportion of the area of aperture 92 that registers with aperture 88.Thus, by rotation of screw 93, the impedance of guide 8| may be matchedwith the internal impedance of amplifier 18.

A similar adjustable gate structure is provided between input wave guidesection 19 and resonator 82, as indicated by the corresponding referencenumerals, for matching the impedanceof guide section 19 to the inputimpedance of resonator 82. f

In operation, ,energy from wave guide section 19 is delivered directlyto excite resonator 82 and `cause velocity modulation of the electronstream. Energy extracted from thel electron stream by resonator 83 isdelivered directly to wave guide :section 8|. Proper impedance match forbest operating conditions is attained by the adjustable gate structures,thereby insuring highly eflicient performance. Hence signal energytraveling from left to right in Figure 2 is relayed and amplied at 'I8with a minimum of losses.

It,will be understood that although the wave guide described herein hasbeen illustrated as being of the hollow-pipe lsingle conductor type.

other types of guide such as dielectric guides or other enclosed-fieldenergy conducting systems may also be used. l

`Since many changes could be made in the above construction and manyapparently Widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. High frequency apparatus comprising a hollow body providing aconductive envelope for enclosing an electromagnetic field, said bodyhaving an aperture in a wall thereof, a pocket vacuum-sealed to saidbody, said pocket having a closed inner end portion within saidenvelopeand having an open end facing said aperture, and said pocket beingpermeable to said field, a movable terminal portion of a high frequencytransmission line extending within said pocket and having a conductiveportion disposed in part within said envelope for coaction with saidfield, and means accessible externally of said body for moving saidterminal portion and varying said coaction with said field.

2. The high frequency apparatus defined vin claim 1, wherein saidterminal portion comprises a conductive coupling loop which is rotatablefor varying its coupling with said field.

3. The high frequency apparatus defined in claim l, wherein saidterminal portion comprises a conductive coupling loop located withinsaid body at a region Where the magnetic field is strong and theelectric field is weak.

4. High frequency apparatus comprising a hollow resonator adapted tocontain an electromagnetic fleld, a high frequency transmission line,means connecting said line to said resonator comprising a conductiveenergy transfer member rotatably connected to said line and extendingwithin said field, means coupled to said member for rotating saidmember, and means permeable to said field sealing off that portion ofsaid resonator in which Isaid member is disposed.

5. High frequency ,apparatus ,comprising a hollow resonator adapted tocontain an electromagnetic eld, a relatively stationary concentricconductor transmission line section, a rotary concentric conductortransmission line section connected between-said resonator and saidstationary line section, a conductive energy transfer loop rigidlysecuredon said rotary line section and coupled with said field, wherebyrotation of said line section produces corresponding rotation of saidloop, and a pocket permeable. to said eld for sealing 01T that portionof said resonator in which said loop is disposed. f

6. An electron discharge device comprising an evacuated hollow resonatoradapted to contain an electromagnetic field, means in said device forpassing a stream of electrons through said eld, a rotatable fieldcoupling member having its inner end physically within said resonatorconnected to said resonator so as to be readily removable with thevacuum seal of the resonator retained unimpaired, and means coupled tosaid member for rotating said member for varying the coupling of saidmember with said field.

7. An electron discharge device comprising an evacuated hollow resonatoradapted to contain an electromagnetic iield, means aligned with saidresonator for passing a stream of electrons resonator with the inner endof said coupler within said resonator and movable with the vacuum sealof the resonator retained unimpaired, and means attached to said couplerfor moving said coupler for varying its coupling with said field.

8. An electron discharge device comprising an evacuated hollow resonatoradapted to contain an electromagnetic field, means disposed on one sideof said resonator for passing a stream of electrons through said field,a rotatable coupler having a loop at its inner end positioned physicallywithin the resonator so as to be coupled to said field, and meanscoupled to said loop for rotating said loop Within said resonator withthe vacuum seal of the resonator retained unimpaired.

9. An electron discharge device comprising an evacuated hollow resonatoradapted to contain an electromagnetic eld, a pocket formationvacuum-sealed with respect to the resonator body having a closed endprojecting into the resonator and an outwardly directed open end, arotatable coupler inserted in said pocket formation having its inner endphysically within the resonator and movable and removable with thevacuum seal of said resonator retained unimpaired, means locatedexterior to said resonator for rotating said coupler, and means alignedWith said resonator for passing an electron stream through said field.

10. High frequency apparatus comprising a concentric transmission linedevice having inner and outer conductors, a hollov.7 resonator adaptedto enclose a magnetic eld, means adjustably coupling one end of saiddevice to said resonator comprising a rotatable energy transfer loopconnecting said conductors and disposed within the physical confines ofsaid resonator, and means coupled to said loop for rotating said loop,so that rotation of said loop varies the coupling between said magneticfield and said device.

11. High frequency apparatus for connecting a high frequency energydevice to a cavity resonator coupled with an electron beam, comprisingmeans for vacuously sealing a section of said resonator traversed bysaid beam, a rotatable energy transfer loop connected to said device andlocated in a nonevacuated section of said reso-` 10 f movable conductiveloop extending into said pocket structure through the open end thereofinto coaction with said field, and means in said device for moving saidloop for varying its coaction with said eld while retaining said vacuumseal of said resonator.

13. High frequency apparatus comprising an evacuated hollow resonator,an aperture in said resonator, means in said apparatus permeable toelectromagnetic energy vacuum-sealing said aperture, means adjacent saidresonator for conveying electromagnetic energy, an adjustable couplingelement at said aperture for coupling electromagnetic energy betweensaid resonator and said conveying means, and means accessible externallyof said resonator for manually adjusting said coupling. k

14. High frequency apparatus comprising a cavity resonator, an aperturein said resonator, means in said apparatus permeable to electromagneticenergy sealing said aperture, means adjacent said aperture conveyingelectromagnetic energy, and an adjustable coupling element at saidaperture for coupling said resonator to said conveying means.

15. High frequency apparatus comprising a source of electrons, means forvelocity modulating electrons emanating from said source resulting ingrouping said electrons, means for extracting electromagnetic energyfrom said grouped electrons, said velocity-modulating means and saidenergy-extracting means including a cavity resonator, said resonatorhaving an aperture, an electromagnetic wave energy conducting meanshaving an aperture, the aperture of said resonator registering with theaperture of said conducting means, and a vitreous vacuum seal positionedin the vicinity of one end of said conducting means, said seal beingpermeable to electromagnetic energy.

W'ILLIAM W. HANSEN.

RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,106,771 Southworth Feb. 1, 19382,153,728 Southworth Apr. 11, 1939 2,190,668 Llewellyn Feb. 20, 19408,200,023 Dallenbach May 7, 1940 2,222,902 `Hahn Nov. 26, 1940 2,237,878Haef Apr. 8, 1941 2,259,690 Hansen et al Oct. 21, 1941 2,287,845 Varianet al. June 3, 1942

